This invention relates to a drum-type thread feeder for a textile machine.
In a known thread feeder of this type (see U.S. Pat. No. 3,883,083) the thread feeder element is designed as a disc brake mounted on a pivotal arm and maintained in an opened position by a stationary brake opening element in the case of positive thread feed. The disk brake thus functionally forms a guide eye which forces the thread to unwind tangentially from the drum, thereby achieving the desired positive feed. The thread brake together with its pivotal arm is adapted to be pivoted manually even into a position below the plane of the thread drum in order to arbitrarily change the device over to intermittent thread feed. A thread control element is disposed radially outside the disc brake forming the thread feed element when seen relative to the drum and is designed as an eye mounted on a pivotal arm. The last-mentioned pivotal arm is spring-loaded and urges the eye upwardly with respect to the plane of the removal edge of the drum, thereby forming a tension compensation loop in the path of thread behind the thread feeder element. If the thread loosens, this tension compensation loop enlarges. It has been found that the loose length of the thread which can be a accommodated in the tension compensation loop in this manner, however, is not sufficient in many cases. The thread drum which continues to rotate for at least a certain time after the thread has loosened pulls the thread along with it at the site of the removal edge and winds it in the wrong direction. In addition to eliminating the original disruption, it is then also necessary to remove the incorrect yarn windings directly above the removal edge, since these would produce an excess supply as soon as the device is started again, thus resulting in another disruption.
It is already known to arrange in a thread feeder the element effecting positive thread feed in the form of an open hook on the side of the drum above the level of the removal edge (see U.S. Pat. No. 3,908,921). The problem of rewinding does not occur there, since the loosened thread is not supported at the level of the removal edge. Due to the low stationary arrangement of the thread guide element, a force component results which is directed downwardly and which acts on the unwinding thread. In the case of yarns which tend to form strong adhesion between adjacent windings due to their fluffiness or for other reasons, there is a danger due to this force component that the second respective winding will be pulled downwardly as well and excess feed will occur. Hence, a device of the type described at the outset, i.e. a thread guide element disposed at the level of the removal edge, is required for such yarns.
The object of the invention is to provide an improved thread feeder of the class described at the outset, i.e. comprising a drum adapted to be set in rotation and associated with a stationary thread guide element disposed at the level of the removal edge for positive thread feed, that such when the thread becomes loose between the textile machine and the feeder, the drum is prevented from winding back the already unwound thread in the wrong direction onto the removal edge area of the drum.
During normal operation, the thread control element is maintained by the tension of the unwinding thread in a position which permits the tangential removal by the stationary thread guide element and thus perfect positive feed. When the removal tension diminishes, the removal site on the removal edge of the thread migrates in the direction of rotation of said drum together with the drum edge. At the same time, the thread is deflected downwardly away from its removal site on the thread edge by means of the descending thread control element. The thread segment extending downwardy away from the drum edge cannot be wound by the drum which continuous to rotate even if it hangs completely loose due to the change in tension. Even if there is no removal of thread from the drum any more and the drum continuous to rotate prior to its standstill or rotates again after an interruption of operation, a thread segment which has a length corresponding to the distance between the thead control element and the most remote site of the drum edge moves similar to a crank in the area beneath the drum. When the textile machine and the drum are started again after elimination of the disruption, the thread control element causes a kind of intermittent thread feed, i.e. the textile machine can initially remove as much yarn from the drum as it requires until normal operating tension has been reached, whereby the thread control element has moved into its corresponding position and thread feed is once again positive. A special advantage of the device in accordance with the invention can be seen in the fact that a very low thread tension can be achieved by the reduction in the site of friction.
In an advantageous embodiment the thread control element is arranged to be pivotal such that it reaches below the base of the drum during its descent movement. The thread segment between the thread control element and the drum edge, which rotates during continued rotation of the drum after the reduction in tension, is thus substantially shorter than if the thread control element were lowered outside the drum. In no case can a loop be formed. In addition, an especially rapid display of disturbances is achieved in the case of this construction due to the movement of the thread control element.
A bent pivotal arm comprising a first leg of a length exceeding the drum height can be provided for the thread control element in an advantageously simple manner. The free end thereof is rotatably mounted on the housing above the drum and outside the projection of the drum periphery in such a way that the leg is movable in a plane which is adjacent the drum and approximately parallel to its longitudinal axis, and that a second leg extends from the first leg substantially toward the drum and forms or supports at its free end the thread control element. Both the pivotal arm and its mounting can be designed in this way to be very simple and economical and require only little space. The path of movement of the thread control element corresponds to a circular arc so that the movement of the thread control element or the pivotal arm can be balanced out in a simple way.
The second leg of the pivotal arm may have a length which is shorter than the distance of the plane of movement of the first pivotal arm from the drum axis. The thread segment between the rotating removal site on the drum edge and the thread control element is thus especially short during the first half rotation after the reduction in tension. If the drum comes to a rapid standstill, the thread will not be pulled back at all by the thread guide element in this way. In addition, a lateral deflection results in addition to the deflection of the thread segment in a downward direction.
In order to regulate the thread tension even during fluctuations in tension, which do not cause complete loosening of the thread, the spring advantageously has such a progressive characteristic that in every position of the pivotal arm the force component urging the thread control element downwardly is substantially equal, i.e. the spring force compensates for the weight components which vary in the different positions of the pivotal arm.
As is the case in all thread feeders, a shut-off means which stops the textile machine and the feeder in the case of disruption, is also required on the device according to the invention. It can be designed and arranged in the known manner. The thread control element, however, can be designed as a shut-off means as well in an especially advantageous manner as is known per se from U.S. Pat. No. 3,883,083. The shut-off function, however, can be arbitrarily deactivated temporarily when the shut-off eye is positioned below the base surface of the drum, thereby restarting the device even if the thread control element is in the shut-off position. This then moves automatically into the operating position again as the tension increases.